Such a device, also known under the term vertex refractometer, is known from the prior art. Generically, a measuring light grid for producing a plurality of light beams is provided in these vertex refractometers. This measuring light grid can be formed, for example, by four light-emitting diodes. The light beams produced by the measuring light grid are deflected by the lens to be studied as a result of refraction of light, the light beams being projected onto a measuring light detector and recorded there electronically. The measuring light grid is projected in a characteristic fashion on the measuring light detector depending on the refraction properties of the lens so that the refraction properties of the lens can be determined from the measurement signals of the measuring light detector. In the generic measuring devices this determination of the refraction properties is made in an evaluation device in which, for example, the illumination pattern recorded using the measuring light detector is evaluated by suitable image processing.
A disadvantage with the known vertex refractometers is that the refraction properties of the lens can always only be studied at one point. For this purpose, for example, the part of the lens to be studied must be placed in the measuring device such that it is located on the principal measurement axis of the measuring device. The refraction properties of the lens can then be determined in this special area. In the case of a regular cylindrical lens, it is sufficient to determine the refraction properties at one point since the refraction properties do not vary over the different areas of the lens.
However, the measurement of irregular lenses, for example, progressive lenses is problematical since in these irregular lenses the refraction properties vary depending on the different areas of the lens. So far, when making measurements of these irregular lenses, it has been necessary for the operator to move the lens by hand between the individual measuring processes in the measuring device and in this way successive measured values are determined for the different areas of the lens. This type of measurement is extraordinarily laborious, inaccurate and cost-intensive.